CN102103747B - Method for calibrating external parameters of monitoring camera by adopting reference height - Google Patents
Method for calibrating external parameters of monitoring camera by adopting reference height Download PDFInfo
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Abstract
The invention discloses a method for calibrating external parameters of a monitoring camera by adopting reference height, which comprises the following steps of: far vanishing point and lower vanishing point-based vision model description and related coordinate system establishment; projected coordinate calculation of reference plumb information-based far vanishing points and lower vanishing points in an image plane; reference height calibration-based camera height, overhead view angle and amplification factor calculation; design of a reference plumb direction-based horizon inclination angle calibration tool; and design and use of perspective projection model-based three-dimensional measurement software and three tools for three-dimensional measurement, namely an equal height change scale, a ground level distance measurement scale and a field depth reconstruction framework. The calibrating method is simple and convenient in operation, quick in calculation and high in measurement precision. The reference can be a pedestrian, furniture or an automobile; and a special ground mark line is not needed. The method allows the camera to be arranged at a low place, and the shooting overhead view angle is slightly upward as long as the bottom of the reference can be seen clearly in the video and the ground level coordinate system is definite.
Description
Technical field
The invention belongs to the intelligent video monitoring technical field, particularly adopt the height of object of reference to carry out the method for video camera calibrating external parameters at monitoring environment, the video camera external parameter that is mainly used under the video monitoring environment is accurately demarcated.
Background technology
The development of Along with computer technology, modern the supervisory system direction of network-orientedization, intellectuality, multi-sourceization gradually develop.Wherein, the intelligent video analysis technology realizes that as video monitoring system intelligentized important means has become the research emphasis of numerous colleges and universities, company or scientific research institution.In recent years, along with improving constantly of computing power, intelligent video technology was widely used in multiple indoor outdoor utility environment such as intelligent transportation, building monitoring, storehouse management; The moving target of monitoring analysis comprises various types of vehicles, pedestrian, parcel object; The major function of monitoring analysis detects from traffic data statistics, vehicle peccancy, to the warning of personnel's abnormal behaviour, article are left over or lose, or the like multiple aspect.Be to be the basis with various video such as Flame Image Process, machine vision, pattern-recognition and image analysis technology, the integrated application integrated system that technology such as collection data transmission technology, control technology, Computer Processing technology combine.
Wherein, Camera calibration is as the important technology of image understanding and machine vision; Whether to the perception of monitoring environment geological information accurate, the system that has influence on comprises to the characteristic of monitoring objective whether the extraction of information such as size, shape, position, movement velocity is correct if directly having influence on system.A good intelligent video monitoring system should be able to be competent at multiple application places, should have the vision mode that can describe general environment.The camera marking method of setting up according to this vision mode also should have the characteristics of versatility, accuracy.
Technical at camera calibration, the worker has proposed many methods both at home and abroad: the someone proposes a kind of multi-point fitting method the earliest, selects a plurality of calibration points repeatedly to demarcate; Each demarcate arc description near calibration point along distance to rate of change; So the described mapping deformation curve of calibration line group is carried out least square fitting and obtains calibration result, but this method has certain limitation, in three dimensions; If this demarcation to the distance to and do; It is unknown that the mapping relations that so highly make progress remain, therefore, and in order to obtain three-dimensional information; Improve simultaneously precision again; The number of calibration line will increase the complexity of system calibrating along with the requirement of precision is increased exponentially, and occurring a large amount of calibration points in the same in addition video also can influence the analysis to single calibration point validity; External parameter is found the solution by the ARGO system of Italy Palma university under the known prerequisite of the inner parameter of supposition video camera; But adopted the method for drawing the grid of a known dimensions on the ground; Utilize its intersection point as calibration point, this method clearly is unfavorable for the popularization of calibration technique; In a lot of practical systems; NICE system for example; Adopted inclination angle, local horizon calibration line and object variation range to describe rectangle; Through setting in the visual field the nearly far away little variation range of object or by the problem of avoiding camera calibration as far as near situation of change, if but not need to target size accurately, calculating this method obviously is fast and effectively; The researchist of Xi'an Communications University adopts on the road surface three parallel lines to confirm the external parameter of vehicle-mounted vidicon as the method for calibration line, and this method clearly has been limited in traffic mark clearly on the highway with the usable range of calibration technique; The researchist of Institute of Automation, CAS analyzes the mapping relations of demarcating line segment and world coordinate system ground level; Only just solved the spacing between 2 of the world coordinate system ground levels with the method for transformation matrix; Though but this method computational accuracy is high; But do not use elevation information, the measurement of the distance between two points that can only demarcate the plane with opposing can not be accomplished real 3 D stereo measurement; The researchist of Nanjing University has adopted multiple algorithm that camera interior and exterior parameter is found the solution one by one; Set up based on the vision mode of end point and carried out tight derivation; But the demarcation means that relied on are six or nine markings that adopted the highway pair of right and left; And this method can only adopt and be positioned at the demarcation line segment that is parallel to each other on the world coordinate system ground level, equally camera calibration The Application of Technology scope has been limited on the clear abundant highway of road mark line.
In practical application, the restriction accurate and scaling method of vision mode is an aspect of camera calibration.Because camera calibration carries out in image, image resolution ratio itself just affects the demarcation degree of accuracy, has brought inevitable error.In addition, the error of staff's timing signal reconnaissance also can have influence on calibration result.Therefore, the needs design is a kind of can satisfy accurate vision mode, and camera marking method convenient to use, reduces personal error as far as possible.
Summary of the invention
The objective of the invention is to, a kind of rig camera calibrating external parameters method that adopts the object of reference height is provided, this method has towards multiple monitoring environment, characteristics such as set-up mode is convenient and swift and the calibration measurements result is accurate.
For achieving the above object, technical solution of the present invention is:
A kind of rig camera calibrating external parameters method that adopts the object of reference height, it sets up world coordinate system from the perspective projection model according to the mounting means of rig camera; Proposed a kind ofly in this world coordinate system, to add the vision mode that end point far away and following end point are described perspective projection deformation, and the mode of on this vision mode basis, setting up world coordinate system, camera coordinate system, image projection coordinate system; The component part of this method comprises following content:
A) based on the coordinate system method for building up of perspective projection model.
B) vision mode of perspective projection deformation is described based on end point far away and following end point.
C) based on the object of reference plumb height calibration point choosing method of above-mentioned model.
D) based on camera height, depression angle, the amplification coefficient computing method of object of reference plumb height.
E) inclination angle, the local horizon calibration tool based on the object of reference vertical designs;
F), comprise the design and use of three kinds of instruments such as object of reference height measuring rule, ground level distance between two points dip stick, the demonstration of depth of field reconstruct framework based on the measurement in space Software Design and the method for application of perspective projection model.
Described rig camera calibrating external parameters method, it comprises the steps:
(a) obtain the video image of rig camera;
(b) in above-mentioned image, seek the object of reference that has obvious vertical information more than two, require two end-point distances of object of reference plummet direction to surpass 15 pixels;
(c), adopt inclination angle, local horizon calibration tool to confirm the inclination angle, local horizon according to the vertical of these objects of reference;
(d) in image, manually mark bottom point and the top point of above-mentioned object of reference, thereby confirm highly to demarcate line segment along vertical;
(e) calculate end point far away and the projection coordinate of following end point in the plane of delineation based on highly demarcating line segment;
(f) go on foot gained end point coordinate according to (e) and highly demarcate line segment calculating video camera setting height(from bottom), depression angle, amplification coefficient;
(g) utilize measurement in space software, whether the setting of check height calibration line is reasonable.
Described rig camera scaling method, its said description with relative coordinate system with the vision mode of following end point based on end point far away is set up, and it sets up mode referring to Fig. 1, comprises the steps:
1) based on perspective projection modelling vision mode; The general angle of setting up in conjunction with rig camera; Proposed to utilize end point far away and following end point to explain the method for perspective projection deformation; That is: in world coordinate system, have such one type of straight line, promptly be parallel to ground level and be parallel to the straight line on the plane of being confirmed by camera optical axis and video camera vertical line, the mapping straight line of all this type straight lines in image can intersect at end point far away; All are parallel to the straight line of camera height pedal line in world coordinate system, and its mapping straight line in image can intersect at end point down; According to above analysis, be the basis with the perspective projection model, introduce two end points and describe perspective deformation, thereby propose new vision mode, and set up world coordinate system, camera coordinate system, image projection coordinate system, like Fig. 1;
2) the world coordinate system coordinate axis is labeled as Xw-Yw-Zw; The initial point of world coordinate system as shown in Figure 1 be positioned at the video camera vertical under; Distance is pointed to a distant place to Yw, intersect with camera optical axis, intersection point corresponding to image center (xc, yc); About point to right-handly to Xw, Xw and Yw have formed ground level; Height is to be set out by initial point to point to the video camera photocentre to Zw, perpendicular to the straight line of ground level; Coordinate in the alive boundary of the video camera photocentre coordinate system is exactly that (0,0, hD), wherein hD is that video camera sets up height;
3) camera coordinate system is an initial point with the video camera photocentre, and when the video camera depression angle is 0, and camera height is 0 o'clock, and video camera is positioned on the world coordinate system initial point straight up; The coordinate axis of camera coordinate system is labeled as Xs-Ys-Zs; Wherein the Xs axle overlaps with the Xw axle, and the Ys axle overlaps with the Yw axle, and the Zs axle overlaps with the Zw axle; When camera height is hD, along Zw axle truck camera coordinate be tied to point (0,0, hD); When the video camera depression angle is alpha, be axle with Xs, the camera coordinate system alpha degree that turns clockwise obtains the camera coordinate system after the conversion, sets up signal like video camera among Fig. 1;
4) calculating of intrinsic parameters of the camera and distortion of camera are corrected, and adopt the gridiron pattern method to solve;
5) initial point of image coordinate system is positioned on the camera optical axis; The plane of delineation is parallel to the picture plane, perpendicular to camera optical axis, shown in shadow region among Fig. 1; The image coordinate system coordinate axis is labeled as X-Y, and Y is identical with Ys axle parallel direction, and X is identical with Xs axle parallel direction; The mapping relations that image coordinate is tied to camera coordinate system depend on the ratio of video camera CCD sampled pixel dot spacing and corresponding imaging point actual pitch; Through combination to several coefficients in the image transformation equation; Finally; Definition picture point pel spacing is to amplification coefficient a, the b of picture plane distance between two points, suppose that video camera along the amplification coefficient of transverse axis and the identical a=b of being of amplification coefficient along vertical axes, so only needs amplification coefficient a of calculating.
Described rig camera scaling method, its said down end point is a point in the image coordinate system, the corresponding point of its world coordinate system are positioned at unlimited distance, just unlimited distance under the video camera photocentre under the world coordinate system Zw direction of principal axis; In image coordinate system, the vertical extended line of all objects all can intersect at down end point, like bottom convergent point among Fig. 2; When video camera was overlooked downwards, object of reference vertical extended line can intersect at a following end point in image; When video camera was upwards looked up, object of reference vertical extended line can intersect at end point, and last end point is positioned at unlimited distance directly over the world coordinate system Zw direction of principal axis equally; Last end point all is positioned on how much with following end point passes the video camera photocentre, on the straight line perpendicular to ground level.The description of end point is referring to Fig. 2 and Fig. 3, and wherein Fig. 3 utilizes the side-looking visual angle to describe the corresponding relation of time end point between world coordinate system and image coordinate system.Described rig camera scaling method, its said end point far away is a point in the image coordinate system, the corresponding point of its world coordinate system are positioned on the local horizon, shown in topmost putting among Fig. 2; Any pair of parallel line that in image, is parallel to ground level all can intersect at some local horizon point, and this point is a perspective deformation end point; End point far away is positioned at through camera optical axis and perpendicular to the plane and the horizontal intersection point of ground level.Fig. 3 utilizes the side-looking visual angle to describe the corresponding relation of end point far away between world coordinate system and image coordinate system.
Described rig camera scaling method, the image coordinate of its said end point far away is on image, to utilize manually to confirm summit and the end point of two above objects of reference along vertical, the calibration line method to set up is referring to Fig. 2 and Fig. 5; Comprise: at first the pixel distance of object of reference summit and end point is carried out normalization according to the height of representative, only move apex coordinate during normalization, end point is constant; Then with any two objects of reference as one group, in image coordinate system, calculate corresponding perspective deformation end point coordinate based on perspective deformation principle; Because this end point is positioned on the local horizon, confirms the local horizon equation with this; The local horizon angle is revised at angle of inclination, local horizon according to obtaining, and in conjunction with the definition of end point far away promptly: end point far away is positioned at through on camera optical axis and the plane perpendicular to ground level, calculates image coordinate, the local horizon of end point far away.
Described rig camera scaling method; Its said camera calibration based on the object of reference plumb height comprises: utilize the end point image coordinate far away of having tried to achieve; And object of reference apex coordinate after the normalization and end point coordinate; Make up two auxiliary straight lines respectively; Fig. 4 visual angle has from the side described the method for drafting of these two boost lines and the position of corresponding intersection point, through analyzing two straight lines and passing camera optical axis and perpendicular to the geometric relationship acquisition simultaneous equations of end point far away with the intersection point on the plane of following end point line:
Xwp1＝Xwp2
Zwp1-Zwp2＝len
Wherein, len is for highly demarcating the height value of line segment representative, and Xwp1, Xwp2, Zwp1, Zwp2 are respectively the world coordinates value of summit line and end point line and midplane intersection point P1, P2, and Fig. 4 visual angle has from the side described the position of these two points; Object of reference height after the substitution normalization is found the solution video camera and is set up height again; Utilize end point coordinate far away and video camera to set up the height calculation result, find the solution amplification coefficient and video camera depression angle in the substitution vision mode.
Described rig camera scaling method, its said inclination angle, local horizon calibration tool design based on the object of reference vertical comprises:
1) adopts the inclination angle, local horizon that instrument is set and confirm the local horizon; The inclination angle, local horizon is provided with instrument and has drawn two reference mark, passes two reference mark and has drawn straight line, and this straight line is represented a straight line parallel with the local horizon, and horizontal inclination angle is represented at its inclination angle; Horizontal relative position is with reference to the top straight line among the figure 2;
2) draw one perpendicular to the 1st) step gained straight line and pass the straight line of picture centre;
3) the 2nd) step gained straight line representes to pass camera optical axis and perpendicular to the projection of plane in image of ground level, this straight line is called the vertical markings;
4) suitable vertical angle is chosen at two of Move tool reference mark in image; The vergence direction that makes vertical markings in the instrument as far as possible with image near the markings object of reference vertical overlaps, perhaps the local horizon markings are tried one's best parallel with the local horizon; It is the deflection angle of turning axle with the optical axis that video camera is set thus.Local horizon instrument method to set up is referring to the straight line of lower end among Fig. 5 and crossing with it vertical dotted line, and two parallel stains are represented the reference mark of instrument.Described rig camera scaling method, its said measurement in space Software Design and method of application based on the perspective projection model comprise: design is based on the measurement in space software operation interface of perspective projection model; And the parameter calibration result that employing the present invention calculates gained carries out the method for checking computations as input through the perspective projection imaging model; According to the checking computations needs, this software comprises: ground level distance between two points survey instrument, object of reference height survey instrument, depth of field reconstruct framework, wait three instruments:
(a) ground level distance between two points survey instrument: two end points in the manual specify image on the ground level, this instrument can show this 2 distances in world coordinate system on the line of two end points; Horizontal line among its demonstration effect such as Fig. 6.
(b) object of reference height survey instrument: vertical line among its metering system such as Fig. 6.This instrument has following usage:
1) manually select the end of object of reference to put and the summit, instrument can calculate and demonstrate the height of object of reference in world coordinate system automatically;
2) upper extreme point at pulling instrument reference mark is specified after the level altitude value, in image, is pasting ground level and is moving this instrument, and the height of this instrument can change with the distance apart from camera; And no matter how the height of this instrument changes, and the height value of its representative is constant;
3) in addition, the straight line that passes the line of two end points of this instrument can point to down end point all the time, and this instrument can remain with the vertical of tested object of reference and overlap when the Measuring Object height;
(c) depth of field reconstruct framework: this instrument is used for checking framework by the world coordinate system of camera calibration parameter reconstruct in the drop shadow effect that image coordinate is fastened, and its effect is referring to Fig. 7; This instrument at first according to the pel spacing of setting in advance, shines upon to world coordinate system; As the unit gap, in world coordinate system, drawn a uniformly-spaced 3D grid with mapping back distance, again this grid projection has been returned in the image; According to whole inclination angle, the size of grid hole and the angle of inclination of grid sidewall of this grid in the image, we can find out roughly whether the framework of reconstruct meets the truth of image scene.The result that on behalf of depth of field reconstruct framework, the grid of rule provide among Fig. 7.Described rig camera scaling method is in its said (b) 2) step, the height of its instrument also can reflect the height that the object of reference that in world coordinate system, has some position, the identical end and have equal height shines upon in image.
Compared with prior art, the present invention only need mark at least two line segments that are positioned at the object of reference plumb height on the ground level, just can accomplish the demarcation of video camera external parameter, need not to delimit in advance surface mark line or placement with reference to supplementary meanss such as scales.Through accurate Geometric Modeling and rigorous mathematical derivation, under the prerequisite that guarantees the calibration measurements precision, simplified demarcating steps, can satisfy the application need of most of monitoring environments.
Description of drawings
Fig. 1 concerns synoptic diagram for three coordinate systems that the present invention set up;
Fig. 2 is the synoptic diagram that concerns between the end point seen from the video camera visual angle and the local horizon;
Fig. 3 is from view end point far away and the mapping relations synoptic diagram of following end point image perpendicular to middle vertical plane;
The boost line adding method synoptic diagram that Fig. 4 is adopted for from the calculating camera height of observing perpendicular to time of middle vertical plane the time;
The example that Fig. 5 chooses for the calibration line that in the practical scene of indoor monitoring, carries out the video camera calibrating external parameters;
Fig. 6 is for to utilize in the measurement in space instrument of the present invention: the application synoptic diagram of height survey instrument and distance measurement tools;
Fig. 7 is the depth of field framework reconstruction result synoptic diagram that utilizes measurement in space instrument of the present invention to obtain.
Embodiment
Please with reference to Fig. 1,2,3,4,5,6 and Fig. 7, the rig camera calibrating external parameters method of employing object of reference height of the present invention: the erection mode according to monitoring environment and video camera has designed high-precision video camera vision mode; Confirm the corresponding relation of world coordinate system 3, camera coordinate system 2 and real world according to the perspective projection model; Utilize end point far away 4, geometrical concept and the real world in end point 5, local horizon 6 interrelate down, confirm the corresponding relation of image coordinate system 1 and world coordinate system 3; In the computing method of calibrating parameters, utilize coordinate transform and the way of adding boost line, in conjunction with projection line segment end points coordinate and the true length 20 of line segment representative of object of reference in image, calculate the height 19 of video camera in world coordinate system; Utilize the height 19 of video camera and the end point coordinate far away in the image coordinate system, demarcate line segment 25, calculate video camera depression angle and video camera amplification coefficient, thereby accomplish the video camera calibrating external parameters in conjunction with the object of reference height of input.
At last, in order to verify the correctness of calibration result, the present invention has designed three kinds of measurement in space instruments: ground level distance between two points survey instrument 29, object of reference height survey instrument 30 and depth of field reconstruct framework instrument 31.Be respectively applied for the distance of measuring on the ground level between two object points, measure the plumb height of object of reference on the ground level, and video scene is carried out the three-dimensional reconstruction of world coordinates framework.Through the high measurement of length and width, and judge with reference to the goodness of fit of object whether video camera amplification coefficient, the isoparametric calculating of camera height be reasonable in framework after the reconstruct and the video.
The rig camera calibrating external parameters method of employing object of reference height of the present invention comprises:
1, with reference to the perspective projection model, coordinate system to set up mode following:
(1) make the coordinate axis of world coordinate system 3 be labeled as: Xw-Yw-Zw; The initial point of world coordinate system as shown in Figure 1 be positioned at the video camera vertical under, distance is pointed to a distant place to coordinate axis Yw, intersects with camera optical axis 14; Intersection point corresponding to image center (xc, yc).About point to right-hand to the direction level of coordinate axis Xw.Coordinate axis Xw and Yw have formed ground level.Coordinate axis Zw is perpendicular to ground level, and its direction is set out by initial point and pointed to the video camera photocentre.The world coordinates of video camera photocentre is exactly 0,0, and hD wherein hD is that video camera sets up height, sets up signal like video camera among Fig. 1.
(2) foundation of world coordinate system 3 is not with reference to the angle of inclination of parallel mark line on the real world ground; World coordinate system is that the rotation of axle is unified mutually with camera coordinate system with the vertical, and has stable angle between the real world ground flat line flag line.
(3) camera coordinate system 2 is an initial point with the video camera photocentre.Suppose when the video camera depression angle be 0, and camera height is 0 o'clock, video camera is positioned on the world coordinate system initial point straight up.The coordinate axis of camera coordinate system is labeled as Xs-Ys-Zs, and wherein the Xs axle overlaps with the Xw axle, and the Ys axle overlaps with the Yw axle, and the Zs axle overlaps with the Zw axle.When camera height is hD, be tied to a little 0,0 along Zw axle truck camera coordinate, hD.When the video camera depression angle is alpha17, be axle with Xs, the camera coordinate system alpha degree 17 that turns clockwise obtains the camera coordinate system after the conversion.
(4) the image coordinate system initial point is positioned on the camera optical axis.The plane of delineation is parallel to the picture plane, and perpendicular to camera optical axis, the image coordinate system coordinate axis is labeled as X-Y, and Y is parallel with the Ys axle, and direction is identical, and X is parallel with the Xs axle, and direction is identical, shown in shadow region among Fig. 1.Image coordinate system 1 depends on the ratio of video camera CCD sampled pixel dot spacing and corresponding imaging point actual pitch to the mapping relations of camera coordinate system 2.Through combination to several coefficients in the image transformation equation; We finally can define amplification coefficient a, the b of picture point pel spacing to picture plane distance between two points; Suppose that video camera is identical with amplification coefficient along vertical axes along the amplification coefficient of transverse axis, so only need to calculate an amplification coefficient a.
(5) according to above-mentioned vision mode we can to obtain from image coordinate system 1 to world coordinate system 3 mapping equation following
The transformation relation that is transformed to image coordinate point from world coordinate point can be rewritten as
In these two relational expressions, after parameter and hD, a, b, α confirmed, these two transformation relations had also just been confirmed.Wherein hD19, α 17 are external parameters, represent the height of video camera and overlook the anglec of rotation.A and b are the amplification coefficients along two axles of image.
(6) have about world coordinate system and can mention below several definition:
Ground level 7: the plane of forming by coordinate system axle Xw and Yw.
Middle vertical plane 8: pass camera optical axis in the world coordinate system and perpendicular to the plane of ground level.
Image axis: the line of image top margin mid point and base mid point.
2, the definition of local horizon and end point and choosing as follows:
(1) described local horizon 6 is straight lines that are parallel to world coordinate system coordinate axis Xw, and local horizon 6 is the set of all perspective projection end points in image.Parallel lines parallel with ground level in the image all can intersect at the some end points on the local horizon 6 in twos.The horizontal line of the top among the description in local horizon 6 such as Fig. 2.
(2) described end point 5 down is positioned at world coordinate system Zw axle, unlimited distance under the direction, just unlimited distance under the video camera photocentre.In image coordinate system 1, the vertical extended line of all objects all can intersect at down end point 5, square doorframe or the corridor post for example vertically installed, and the extended line in its image coordinate system can intersect at down end point 5.This point is positioned on the middle vertical plane, and it is the same all can to intersect on the local horizon certain end point in twos as parallel lines all in the image, and when video camera was overlooked downwards, object of reference vertical extended line can intersect at down end point; When video camera was upwards looked up, object of reference vertical extended line can intersect at end point.Last end point is positioned at same with following end point and passes on the straight line of video camera photocentre perpendicular to ground level on how much.Among the description of following end point 5 such as Fig. 3 by under intersection point.Oblique line among Fig. 3 Fig. 4 is represented a plane 15 that is parallel to the plane of delineation, is the symmetrical mapping of the plane of delineation about the video camera photocentre.
(3) described end point far away 4 is positioned in image coordinate system on the local horizon (6).In world coordinate system, in middle vertical plane 8, making a straight line that passes the video camera photocentre and be parallel to ground level is eye-level display 16, and the extreme point that this straight line extends to unlimited distance always is exactly the implication of end point 4 far away in world coordinate system.In image coordinate system 1, end point far away is exactly this straight line and horizontal intersection point.Rotate when video camera has side direction, during over against the shooting highway, end point far away just coincides with the perspective deformation end point of the parallel lane line of highway.Description such as Fig. 3 right-of-center in political views's top-cross point of end point far away.
3, confirm that video camera is along the optical axis deflection angle
When preparing that rig camera is carried out timing signal, at first should confirm the deflection angle of video camera along optical axis, this deflection angle causes passing in image axis and the world coordinate system has a stable angle between the vertical plane of optical axis perpendicular to ground level.Can claim that this angle is the angle of inclination of local horizon in image, because video camera possibly be to be placed with at any angle, so this angle is very important.
Utilize the inclination angle, local horizon that instrument 27 is set and set this deflection angle.Two reference mark 28 that 2 conducts are parallel to horizontal straight line are chosen in suitable position in image, move the angle of two these straight lines of some adjustment respectively.Instrument can be drawn one and represent the intersection of the middle vertical plane and the plane of delineation perpendicular to the green straight line of this straight line in image, the local horizon in the world coordinate system should be perpendicular to this straight line, and is parallel to the line at two reference mark.The description in local horizon 6 is referring to the top horizontal line among Fig. 2.
In addition, according to the perspective projection image-forming principle, the object in the green line both sides should have opposite angle of inclination.After the perspective projection image transformation, the object in the visual field has nearly far away little characteristics.The object vertical extended line of both sides can point to same end point and just descend end point 5 when video camera is overlooked; The vertical extended line of both sides object can point to the same end point that goes up when video camera is looked up.Therefore the deflection along optical axis does not take place when if video camera is installed, so all can be to tilt in the projection of object in image of the video camera left and right sides.We can utilize this drop shadow effect, select appropriate control point position, and the object that makes end point far away and following end point line both sides is all to tilt, thereby definite video camera is along the deflection angle of optical axis.About the synoptic diagram of calibration tool and scaling method referring to Fig. 5, the setting of calibration line.
4, choose object of reference height calibration line
In image, because perspective deformation, can be to tilt at the object of image both sides.When selecting object of reference height calibration line end points, should abide by this deformation effect and select rational calibration point position.The pedestrian who supposes 175 centimetres of heights are arranged in the visual field is through out-of-date, and we carry out the video grabgraf when he walks about; The mid point of getting between the bipod is an end point, and the crown is the summit; The height of importing this people afterwards is 175 centimetres, has so just accomplished a calibration line.Because perspective deformation, when video camera is overlooked shooting, though this people on image left side or right side, the mid point range image axis of two pin lines all can be nearer than a range image axis.We only need to abide by these actual conditions, in image, mark the actual position on end point and summit 26.The error of demarcating like this is just from image resolution ratio with to the accuracy of estimation of true altitude value.
Usually we select at least two height to demarcate line segment, and this can adopt and from the visual field, seek moving target, repeatedly the sectional drawing way of demarcating; Also can select a plurality of actual stationary bodies in the surround of a comparison field, estimate its true altitude, demarcate.Choosing of height calibration line 9 referring to Fig. 2 and Fig. 5.
For the calculating of back, we also will form row with the height calibration line, and sort according to end point coordinate.Then, the height calibration line is carried out normalization: will represent the calibration line group of differing heights to be converted into the calibration line group of representing equal height.
5, calculate end point coordinate far away
To analyzing through the height calibration line group after the height normalization.Appoint and to get wherein two height and demarcate line segment, two summits are connected to form straight line L1, again end point is connected to form another straight line L2.Because these two straight lines are parallel lines in world coordinate system, and L2 is arranged in ground level, and so, these two straight lines can intersect at some end points on the local horizon in image coordinate system.If we are provided with the height calibration line more than 2 in this image, just can be through organizing and solve a plurality of end points in twos.Coordinate through these end points of match we can be in the hope of the equation of local horizon in image coordinate system, and obtain the inclination angle of local horizon in image according to this equation, the video camera that is used to revise the front input is along the optical axis deflection angle.Fig. 2 has described the position of end point 4 far away image from positive visual angle, Fig. 3 utilizes the side-looking visual angle to describe the corresponding relation of end point 4 far away between world coordinate system 3 and image coordinate system 1.End point 4 far away is positioned on the image axis, the intersection point that end point far away is exactly middle vertical plane 8 and local horizon 6 in image coordinate system.Because video camera causes that along the deflection of optical axis a stable angle is arranged between axis and the world coordinate system middle vertical plane; After revising according to this deflection angle reverse rotation image coordinate system; We just can be in the hope of the coordinate of end point far away, and the pixel distance at end point 4 range image centers far away.
According to 3 mapping equation (1) is as follows from image coordinate system 1 to world coordinate system
Can find out that from following formula image coordinate y and world coordinates Yw are one to one.Work as y-y
cDuring=a cot α, X
w→ ∞, Y
w→ ∞ that is to say, y
f=a cot α+y
cRepresent the image coordinate of an infinity point, i.e. an end point on the local horizon, and y
fIt is exactly horizontal vertical component.Therefore, if we can obtain horizontal vertical component through other means, we just can instead release:
a?cotα＝y
t-y
c …………………………………………………………(3)
Following formula is represented end point far away and the relation of distance between amplification coefficient and video camera depression angle.In image coordinate, y
cCorresponding picture centre, a cot α corresponding from the picture centre point coordinate to horizontal vertical range.
On the other hand, work as y-y
cDuring=atan α, Y
w=0, promptly the pairing image coordinate vertical component of the initial point of world coordinate system also is simultaneously the vertical component coordinate y of following end point
d
Therefore, the coordinate of end point far away is (x
c, y
t), y wherein
t=a cot α+y
cThe coordinate of following end point is (x
c, y
d), y wherein
d=atan α+y
c
6, calculate camera height
In the world coordinate system, we are referred to as midplane to be parallel to local horizon and the plane through the video camera photocentre perpendicular to middle vertical plane.
To any height calibration line 25, its summit is that X1 21, X2 22 analyze, and draws two boost lines 23,24 respectively through the summit 21 and the end point 22 of markings from end point far away, and these two boost lines and midplane intersect at a P1 and P2.Because these two boost lines are represented the parallel lines in a pair of world coordinate system; So in world coordinate system; These two lines not only are parallel to each other, and are parallel to middle vertical plane, and we set up equality according to P1 and P2 relation on how much in world coordinate system according to the perspective transform equation so; Height value after the substitution normalization is tried to achieve camera height 19.Fig. 4 visual angle has from the side described the method for drafting of these two boost lines 23,24 and the position of corresponding intersection point.
On the other hand, owing to set a plurality of height calibration lines, we can solve a plurality of height values, to the result of calculation of these results averaged as camera height.
Equipment choosing demarcate apex coordinate be (x1, y1), the P1 coordinate (xp1, yp1), far the end point coordinate (x0, y0).So:
(y1-y0)/(x1-x0)＝(yp1-y0)/(xp1-x0)
Wherein yp1=picture altitude/2 are found the solution xp1 like this.In like manner try to achieve (xp2, yp2).According to shining upon formula:
Known conditions is:
Xwp1＝Xwp2，
Zwp1-Zwp2＝len
Wherein len is a height value of demarcating the line segment representative.
The coordinate figure of substitution P1, P2 in Xwp1=Xwp2 has just obtained camera height hD.
7, calculate video camera depression angle and amplification coefficient
In the perspective projection imaging model, the antenna height 19 and the depression angle 17 of video camera are the most basic external parameters, and there is certain functional relation in the image coordinate itself of depression angle 17 and end point 4 far away.
y
t＝a?cotα+y
c
Analysis perspective projection imaging coordinate system conversion formula, we can extract the funtcional relationship between depression angle 17 and the end point 4 far away.Simultaneously, under the situation of camera height, we can obtain another conversion equality again according to the image mapped coordinate known, and so simultaneous solves depression angle and amplification coefficient.
In like manner, owing to be provided with a plurality of demarcation line segments in advance, can calculate manyly to the result, we average as output.Accomplish the calculating of video camera external parameter.
8, measure calibration result
Whether accurate in order to verify demarcation output, we have designed the measurement in space Software tool based on the perspective projection model, adopt the perspective projection imaging model to carrying out checking computations based on parameter calibration result of the present invention.This software comprises three instruments:
1) ground level distance between two points survey instrument 29.Through two end points on the ground level in the manual specify image, this instrument can show this 2 distances in world coordinate system on the line of two end points.Its measurement effect is referring to the horizontal line of band numeral among Fig. 6.
2) object of reference height survey instrument 30.Its measurement effect is referring to the vertical line of band numeral among Fig. 6.This instrument has two kinds of usages:
(a) at first, manually select the end point and the summit of object of reference, instrument can calculate and demonstrate the height of object of reference in world coordinate system automatically;
(b) secondly, specify after the level altitude value at pulling instrument reference mark, in image, is pasting ground level and moving this instrument, and the height of this instrument can change with the distance apart from camera; And no matter how the height of this instrument changes, and the height value of its representative is constant.Its height also can reflect the height that the object of reference that in world coordinate system, has some position, the identical end and have equal height shines upon in image.
(c) in addition, the straight line that passes the line of two end points of this instrument can point to down end point all the time, and this instrument can remain with the vertical of tested object of reference and overlap when the Measuring Object height.
3) depth of field reconstruct framework 31: this instrument is used for checking framework by the world coordinate system of camera calibration parameter reconstruct in the drop shadow effect that image coordinate is fastened, and its effect is referring to Fig. 7; This instrument at first according to the pel spacing of setting in advance, shines upon to world coordinate system.As the unit gap, in world coordinate system, drawn a uniformly-spaced 3D grid with mapping back distance, again this grid projection has been returned in the image.According to whole inclination angle, the size of grid hole and the angle of inclination of grid sidewall of this grid in the image, we can find out roughly whether the framework of reconstruct meets the truth of image scene.The result that on behalf of depth of field reconstruct framework, the grid of rule provide among Fig. 7.
Scaling method provided by the invention is easy and simple to handle, and computing is quick, and measuring accuracy is high.Design of the present invention has taken into full account various possible rig camera mounting meanss; Is input parameter with object of reference in the scene apart from the height of ground level; Object of reference can be pedestrian, furniture or automobile; Do not rely on special ground markings, be applicable to multiple monitoring places such as indoor, square, road.In addition; The present invention does not require that the necessary level of the depression angle that video camera is installed is downward, and video camera can be installed on the short physical features such as desk, and depression angle can make progress slightly; As long as in video, can see the object of reference bottom clearly, plane coordinate system gets final product clearly.
Claims (4)
1. rig camera calibrating external parameters method that adopts the object of reference height is characterized in that:
From the perspective projection model, set up world coordinate system according to the mounting means of rig camera; Proposed a kind ofly in this world coordinate system, to add the vision mode that end point far away and following end point are described perspective projection deformation, and the mode of on this vision mode basis, setting up world coordinate system, camera coordinate system, image projection coordinate system; The ingredient of this method comprises following content:
Coordinate system method for building up based on the perspective projection model;
The vision mode of perspective projection deformation is described based on end point far away and following end point;
Object of reference plumb height calibration point choosing method based on above-mentioned model;
Camera height, depression angle, amplification coefficient computing method based on the object of reference plumb height;
Inclination angle, local horizon calibration tool design based on the object of reference vertical;
Based on the measurement in space Software Design and the method for application of perspective projection model, comprise the design and use of three kinds of instruments such as object of reference height measuring rule, ground level distance between two points dip stick, the demonstration of depth of field reconstruct framework;
Wherein, this rig camera calibrating external parameters method comprises the steps:
(a) obtain the video image of rig camera;
(b) in above-mentioned image, seek the object of reference that has obvious vertical information more than two, require two end-point distances of object of reference plummet direction to surpass 15 pixels;
(c), adopt inclination angle, local horizon calibration tool to confirm the inclination angle, local horizon according to the vertical of these objects of reference;
(d) in image, manually mark bottom point and the top point of above-mentioned object of reference, thereby confirm highly to demarcate line segment along vertical;
(e) calculate end point far away and the projection coordinate of following end point in the plane of delineation based on highly demarcating line segment;
(f) go on foot gained end point coordinate according to (e) and highly demarcate line segment calculating video camera setting height(from bottom), depression angle, amplification coefficient;
(g) utilize measurement in space software, whether the setting of check height calibration line is reasonable;
Wherein, the said description with relative coordinate system with the vision mode of following end point based on end point far away set up, and comprises the steps:
(1) based on perspective projection modelling vision mode; The general angle of setting up in conjunction with rig camera; Proposed to utilize end point far away and following end point to explain the method for perspective projection deformation; That is: in world coordinate system, have such one type of straight line, promptly be parallel to ground level and be parallel to the straight line on the plane of being confirmed by camera optical axis and video camera vertical line, the mapping straight line of all this type straight lines in image can intersect at end point far away; All are parallel to the straight line of camera height pedal line in world coordinate system, and its mapping straight line in image can intersect at end point down; According to above analysis, be the basis with the perspective projection model, introduce two end points and describe perspective deformation, thereby propose new vision mode, and set up world coordinate system, camera coordinate system, image projection coordinate system;
(2) the world coordinate system coordinate axis is labeled as Xw-Yw-Zw; The initial point of world coordinate system be positioned at the video camera vertical under; Distance is pointed to a distant place to Yw, intersect with camera optical axis, intersection point corresponding to image center (xc, yc); About point to right-handly to Xw, Xw and Yw have formed ground level; Height is to be set out by initial point to point to the video camera photocentre to Zw, perpendicular to the straight line of ground level; Coordinate in the alive boundary of the video camera photocentre coordinate system is exactly that (0,0, hD), wherein hD is that video camera sets up height;
(3) camera coordinate system is an initial point with the video camera photocentre, and when the video camera depression angle is 0, and camera height is 0 o'clock, and video camera is positioned on the world coordinate system initial point straight up; The coordinate axis of camera coordinate system is labeled as Xs-Ys-Zs; Wherein the Xs axle overlaps with the Xw axle, and the Ys axle overlaps with the Yw axle, and the Zs axle overlaps with the Zw axle; When camera height is hD, along Zw axle truck camera coordinate be tied to point (0,0, hD); When the video camera depression angle is alpha, be axle with Xs, the camera coordinate system alpha degree that turns clockwise obtains the camera coordinate system after the conversion;
(4) calculating of intrinsic parameters of the camera and distortion of camera are corrected, and adopt the gridiron pattern method to solve;
(5) initial point of image coordinate system is positioned on the camera optical axis; The plane of delineation is parallel to the picture plane, perpendicular to camera optical axis; The image coordinate system coordinate axis is labeled as X-Y, and Y is identical with Ys axle parallel direction, and X is identical with Xs axle parallel direction; The mapping relations that image coordinate is tied to camera coordinate system depend on the ratio of video camera CCD sampled pixel dot spacing and corresponding imaging point actual pitch; Through combination to several coefficients in the image transformation equation; Finally; Definition picture point pel spacing is to amplification coefficient a, the b of picture plane distance between two points, suppose that video camera along the amplification coefficient of transverse axis and the identical a=b of being of amplification coefficient along vertical axes, so only needs amplification coefficient a of calculating;
Said down end point is a point in the image coordinate system, and the corresponding point of its world coordinate system are positioned at unlimited distance, just unlimited distance under the video camera photocentre under the world coordinate system Zw direction of principal axis; In image coordinate system, the vertical extended line of all objects all can intersect at down end point; When video camera was overlooked downwards, object of reference vertical extended line can intersect at a following end point in image; When video camera was upwards looked up, object of reference vertical extended line can intersect at end point, and last end point is positioned at unlimited distance directly over the world coordinate system Zw direction of principal axis equally; Last end point all is positioned on how much with following end point passes the video camera photocentre, on the straight line perpendicular to ground level;
Said end point far away is a point in the image coordinate system, and the corresponding point of its world coordinate system are positioned on the local horizon; Any pair of parallel line that in image, is parallel to ground level all can intersect at some local horizon point, and this point is a perspective deformation end point; End point far away is positioned at through camera optical axis and perpendicular to the plane and the horizontal intersection point of ground level;
The image coordinate of said end point far away is on image, to utilize manually to confirm summit and the end point of two above objects of reference along vertical; Comprise: at first the pixel distance of object of reference summit and end point is carried out normalization according to the height of representative, only move apex coordinate during normalization, end point is constant; Then with any two objects of reference as one group, in image coordinate system, calculate corresponding perspective deformation end point coordinate based on perspective deformation principle; Because this end point is positioned on the local horizon, confirms the local horizon equation with this; The local horizon angle is revised at angle of inclination, local horizon according to obtaining, and in conjunction with the definition of end point far away promptly: end point far away is positioned at through on camera optical axis and the plane perpendicular to ground level, calculates the image coordinate of end point far away;
Said camera calibration based on the object of reference plumb height comprises: utilize the end point image coordinate far away of having tried to achieve; And object of reference apex coordinate after the normalization and end point coordinate; Make up two auxiliary straight lines respectively, through analyzing two straight lines and passing camera optical axis and perpendicular to the geometric relationship acquisition simultaneous equations of end point far away with the intersection point on the plane of following end point line:
Xwp1＝Xwp2
Zwp1-Zwp2＝len
Wherein, len is for highly demarcating the height value of line segment representative, and Xwp1, Xwp2, Zwp1, Zwp2 are respectively the world coordinates value of summit line and end point line and midplane intersection point P1, P2; Object of reference height after the substitution normalization is found the solution video camera and is set up height again; Utilize end point coordinate far away and video camera to set up the height calculation result, find the solution amplification coefficient and video camera depression angle in the substitution vision mode.
2. rig camera scaling method according to claim 1 is characterized in that: said inclination angle, local horizon calibration tool design based on the object of reference vertical comprises:
1) adopts the inclination angle, local horizon that instrument is set and confirm the local horizon; The inclination angle, local horizon is provided with instrument and has drawn two reference mark, passes two reference mark and has drawn straight line, and this straight line is represented a straight line parallel with the local horizon, and horizontal inclination angle is represented at its inclination angle;
2) draw one perpendicular to the 1st) step gained straight line and pass the straight line of picture centre;
3) the 2nd) step gained straight line representes to pass camera optical axis and perpendicular to the projection of plane in image of ground level, this straight line is called the vertical markings;
4) suitable vertical angle is chosen at two of Move tool reference mark in image, and near the object of reference vertical in the vergence direction that makes vertical markings in the instrument and the image markings overlaps, and perhaps the local horizon markings are parallel with the local horizon; It is the deflection angle of turning axle with the optical axis that video camera is set thus.
3. rig camera scaling method according to claim 1 is characterized in that: said measurement in space Software Design and method of application based on the perspective projection model comprise: design is based on the measurement in space software operation interface of perspective projection model; And the parameter calibration result that employing the present invention calculates gained carries out the method for checking computations as input through the perspective projection imaging model; According to the checking computations needs, this software comprises: ground level distance between two points survey instrument, object of reference height survey instrument, depth of field reconstruct framework, wait three instruments:
(a) ground level distance between two points survey instrument: two end points in the manual specify image on the ground level, this instrument can show this 2 distances in world coordinate system on the line of two end points;
(b) object of reference height survey instrument: this instrument has following usage:
1) manually select the end of object of reference to put and the summit, instrument can calculate and demonstrate the height of object of reference in world coordinate system automatically;
2) upper extreme point at pulling instrument reference mark is specified after the level altitude value, in image, is pasting ground level and is moving this instrument, and the height of this instrument can change with the distance apart from camera; And no matter how the height of this instrument changes, and the height value of its representative is constant;
3) in addition, the straight line that passes the line of two end points of this instrument can point to down end point all the time, and this instrument can remain with the vertical of tested object of reference and overlap when the Measuring Object height;
(c) depth of field reconstruct framework: this instrument is used for checking by the framework of the world coordinate system of camera calibration parameter reconstruct in drop shadow effect that image coordinate is fastened; This instrument at first according to the pel spacing of setting in advance, shines upon to world coordinate system; As the unit gap, in world coordinate system, drawn a uniformly-spaced 3D grid with mapping back distance, again this grid projection has been returned in the image; According to whole inclination angle, the size of grid hole and the angle of inclination of grid sidewall of this grid in the image, we can find out roughly whether the framework of reconstruct meets the truth of image scene.
4. rig camera scaling method according to claim 3; It is characterized in that: in said (b) 2) step, the height of its instrument also can reflect the height that the object of reference that in world coordinate system, has some position, the identical end and have equal height shines upon in image.
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